It is very unlikely that we can ever hope to understand
how each of the hundred billion neurons in the brain contribute to the
functioning of the nervous system. However, neuroscientists have devised several
ways of categorizing neurons that will make their roles easier to understand.

Neurites:

Neurons can be classified by the number of neurites
(axons and dendrites) that extend from the cell body (soma). Cells can be unipolar,
bipolar, or multipolar.

Dendrites:

Dendritic trees can vary widely between neurons. In
the cerebral cortex, there are two types: pyramidal cells (pyramid
shaped) and stellate cells (star shaped). Cells can also be
classified by whether the dendrites have spines or not. Those that do are
called spiny and those that don't are called aspinous.
Pyramidal cells are spiny, while stellate cells can be spiny or aspinous.

Connections:

Neurons can be classified based on their connections
to different tissue types in the body. Neurons that have connections to
sensory surfaces, such as the skin, are primary sensory neurons.
Neurons that form synapses with muscles are motorneurons. However,
most neurons form connections with other neurons - these are the interneurons.

Axon Length:

Neurons can be differentiated based on how long of
an axon they have. Neurons with very long axons that extend from on
area of the brain to another are the Golgi Type I, while those with
short, local circuit axons are the Golgi Type II.

Neurotransmitter:

Aside from neuron morphology, neurons can also be
classified based on their chemistry - the neurotransmitter(s)
they release. For example, neurons that release acetylcholine are called cholinergic
neuron.

Created and Maintained by: Melissa
Davies
Last Updated: April 09, 2002 08:58 PM